Perforated tissue graft

ABSTRACT

A tissue graft for soft tissue repair or reconstruction comprising a sheet of a biopolymer-based matrix having a plurality of small perforations and a plurality of large perforations. The small perforations are sized to facilitate clotting and granulation tissue development within the perforations which, in turn, facilitates revascularization and cell repopulation in the patient. The large perforations are sized to reduce the occurrence of clotting and granulation tissue development within the perforations so that extravascular tissue fluids accumulating at the implant site can drain through the tissue graft. The large perforations enhance mammal tissue anchoring by permitting mammal tissue to compress into the perforations increasing mammal tissue contact area.

BACKGROUND

The present invention relates to the field of tissue engineering, and inparticular to animal-derived, bioremodelable, biopolymer scaffoldmaterials used to repair animal tissue.

In the field of tissue engineering, the following three components areused alone or in combination to repair or create new tissue and organsubstitutes: 1) scaffolds made of naturally-occurring polymers (e.g.collagens), man-made polymers, (e.g. PTFE, Dacron, PET or polyethylene)or self-degrading, man-made polymers (e.g. PLA or PGA); 2) signalingmolecules that give developmental instructions to cells; and 3) cells.

Man-made implant materials such as synthetic polymers, plastics, andsurface-coated metals may have different degrees of immunogenicity andsuffer from significant limitations that prohibit their broadapplications. A major limitation is that cells cannot remodel them afterimplantation. They may be susceptible to microbial infection, and someundergo calcification.

Decellularized animal tissues comprise scaffolds made ofnaturally-occurring polymer. Decellularized animal tissues anddecellularization processes are described in U.S. Pat. Nos. 9,011,895,7,354,702, and 6,696,074, each of which is hereby incorporated byreference in its entirety. The patents describe methods of forming andpreserving a bioremodelable, biopolymer scaffold material by subjectinganimal tissue, for example fetal or neo-natal bovine dermis tissue, tochemical and mechanical processing. The resulting product ischaracterized by its microbial, fungal, viral and prion inactivatedstate, and it is strong, bioremodelable, drapable and does not undergocalcification. Such decellularized animal tissues have broadapplicability in clinical applications. PRIMATRIX Dermal Repair Scaffoldand SURGIMEND Collagen Matrix (TEI Biosciences, Inc., Waltham, Mass.)are examples of decellularized animal tissues on the market.

Holes or gaps have been placed in tissue grafts to allow fluid drainage,substance or cell passage, and/or graft material expansion. For example,PRIMATRIX Dermal Repair Scaffolds are offered on the market in meshedand fenestrated configurations in addition to the solid configuration.

Although various tissue graft materials are available commercially,there remains a need for tissue grafts that have improved physicalproperties and effectiveness for tissue repair, regeneration, andreconstruction.

SUMMARY

Briefly and in general terms, the present invention provides tissuegrafts such as decellularized tissue products having perforations of atleast two different sizes. The introduction of perforations of selectedsizes in decellularized tissue products modulates the biologicproperties of the implant. More specifically, the size of theperforation affects local fluid collection/removal, revascularization,tissue generation, and tissue remodeling characteristics.

In accordance with an aspect of the present invention, a tissue graftfor repair or reconstruction of tissue of a mammal is provided. Thetissue graft comprises a sheet of a biopolymer-based matrix having aplurality of small perforations and a plurality of large perforations,wherein the small perforations are smaller in size than the largeperforations. The creation of specific hole patterns within the tissuegraft directs different biological responses by location within thedevice. Surgical site fluid drainage, tissue regeneration and woundhealing is controlled by altering the size, and location of perforationsin the tissue graft.

In accordance with another aspect of the present invention, there isprovided a method for repair or reconstruction of soft tissue byapplying a tissue graft to a patient in need of the treatment, whereinthe tissue graft has a specific hole pattern that directs differentbiological responses within the device. More specifically, the method ofrepairing or constructing tissue in a patient, comprises providing atissue graft comprising a sheet of a tissue graft material and having aplurality of small perforations and a plurality of large perforations,wherein the small perforations are smaller in size than the largeperforations; applying the tissue graft to the patient at an implantsite; allowing revascularization and cell repopulation in the patient;and applying surgical drains or negative pressure wound therapy toremove extravascular tissue fluids from the implant site in theperioperative and early postoperative period.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the invention, whentaken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein with referenceto the drawings, in which:

FIG. 1 is a top plan view of an embodiment of a tissue graft inaccordance with the present invention; and

FIG. 2 is a schematic diagram and visual representation of perforationsabove and below the size threshold.

DETAILED DESCRIPTION OF CERTAIN EXEMPLARY EMBODIMENTS

The present disclosure relates to tissue grafts having perforations ofat least two different sizes for repair or reconstruction of softtissue. Embodiments of the presently disclosed tissue grafts will bedescribed in detail with reference to the drawings.

The terms “tissue graft” and “tissue graft material” as used hereinrefer to an implant or repair material derived from tissue, includingautograft, allograft or xenograft tissues, materials engineered frommaterials originated from human or animal tissue, and combinations ofthe foregoing. Examples of tissue grafts and tissue graft materialsinclude decellularized animal tissue, engineered collagen matrices, andhuman placental tissue.

The term “perforation” as used herein refers to an aperture passingthrough something, or an act of making an aperture on something. Aperforation can be of any shape or size. The terms “perforation”,“opening”, “hole”, “gap”, “void”, “pore”, and “aperture” may be usedherein interchangeably.

The term “sheet” as used herein refers to a broad, relatively thin,surface or layer of a material. Such sheets may be flat or uniform inthickness or may vary in thickness across their surfaces and may be ofany shape.

As used herein, transitional phrases such as “comprising”, “including”,“having”, “containing”, “involving”, “composed of”, and the like are tobe understood to be open-ended and to mean including but not limited to.

The indefinite articles “a” and “an”, as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one”.

The term “about” as used herein indicates that a value can vary by up to±10%, for example, ±5%, ±2% or ±1%.

In accordance with an aspect of the present invention, a tissue graft isprovided that comprises a sheet of a tissue graft material having aplurality of small perforations and a plurality of large perforations,wherein the small perforations are smaller in size than the largeperforations.

The tissue graft material may be an acellular collagen matrix derivedfrom fetal or neonatal bovine dermis. A sheet of a naturally occurring,biopolymer-based matrix may be produced from animal tissue by a processcomprising the following steps: (1) removing the tissue from its animalsource and then removing the flesh from the tissue; (2) optionallyextracting growth and differentiation factors from the tissue; (3)inactivating infective agents of the tissue, for example, by treatingwith NaOH; (4) mechanically applying pressure to remove undesirablecomponents from the tissue; (5) washing the tissue for removal ofchemical residues; (6) optionally drying, for example, lyophilizing; and(7) optionally cross-linking the tissue after chemical and mechanicaltreatment; (8) optionally cutting the tissue into desired shapes andsizes; and (9) optionally terminally sterilizing. See, for example, U.S.Pat. No. 9,011,895, which is incorporated herein by reference in itsentirety. To produce the tissue graft of the present invention, anadditional step is included in the process to add particularly sizedperforations during the process, for example, after the drying step,after the cross-linking step, or after the cutting step. The perforatingstep will be described in more detail below.

Another example of a tissue graft material is an engineered collagenmatrix. A sheet of an engineered collagen matrix may be produced from aprocess comprising the steps: (1) preparing a dispersion of collagen(for example, bovine tendon collagen); (2) optionally addingglycosaminoglycan (GAG) to the collagen dispersion; (3) lyophilizing thecollagen or collagen/GAG dispersion to dryness; (4) optionally applyinga silicone layer to the lyophilized collagen or collagen/GAG material;(5) optionally cross-linking the lyophilized collagen or collagen/GAGmaterial; (6) optionally cutting the tissue into desired shapes andsizes; and (7) optionally terminally sterilizing. See, for example, U.S.Pat. No. 6,969,523, which is incorporated herein by reference in itsentirety. To produce the tissue graft of the present invention, anadditional step is included in the process to add particularly sizedperforations during the process, for example, after the lyophilizingstep, after the applying a silicone layer step, after the cross-linkingstep, or after the cutting step. The perforating step will be describedin more detail below.

It should also be understood that, unless clearly indicated to thecontrary, in any process or methods described or claimed herein thatinclude more than one step or act, the order of the steps or acts of themethod is not necessarily limited to the order in which the steps oracts of the method are recited. The order of steps or acts may beadjusted by those skilled in the art.

FIG. 1 depicts an exemplary embodiment of a tissue graft of the presentinvention. The tissue graft 10 comprises a sheet of a tissue graftmaterial, for example, acellular dermis from fetal and neonatal bovinetissue, having a plurality of small perforations 110 and a plurality oflarge perforations 120. The small perforations 110 are smaller in sizethan the large perforations 120. The small and large perforations arecircular or substantially circular. The small perforations have adiameter of about 2 mm and speed surgical mesh revascularization andcell repopulation. The large perforations have a diameter of about 3 mmand improve tissue anchoring by permitting patient muscle tissue tocompress into the perforations of larger diameter, thus allowingincreased contact area, and more rapid attachment or sealing topotentially reduce seroma. The tissue graft of the embodiment is about 2mm thick. The small perforations of about 2 mm in diameter have an openarea of 3.14 mm² and a void volume of about 6.28 mm³. The largeperforations of about 3 mm in diameter have an open area of 7.07 mm² anda void volume of about 14.14 mm³. The tissue graft includingperforations of two sizes permits drainage/removal of tissue fluidsproduced as a result of local tissue trauma.

The tissue graft may have a thickness in the range of about 0.5 mm toabout 4.5 mm and preferably in the range of about 2 mm to about 4 mm.

The small perforations may be about 1 mm to about 2.5 mm in diameter,and the large perforations may be about 2.5 mm to about 4 mm indiameter. The small perforations and the large perforations havediameters in the ratio of about 1:1.2 to about 1:2 and preferably about1:1.3 to about 1:1.7, for example about 1:1.5.

Although the embodiment depicted in the drawing has circularperforations, it is contemplated that the perforations can have anyshape, such as oval, square, rectangular, diamond or any irregular orother shape. The small perforations and the large perforations have openareas in the ratio of about 1:1.5 to about 1:3, and preferably about 1:2to about 1:2.5, for example about 1:2.25. The small perforations and thelarge perforations have void volumes in the ratio of about 1:1.5 toabout 1:3, and preferably about 1:2 to about 1:2.5, for example about1:2.25.

The small perforations are sized to facilitate fibrin provisional matrixformation (clotting) and granulation tissue development within theperforations which, in turn, is a source of blood vessels and cells tofacilitate revascularization and cell repopulation of the tissue graftimplanted on the mammal. The large perforations are sized to reduce theoccurrence of fibrin provisional matrix formation and granulation tissuedevelopment within the perforations so that extravascular tissue fluidsaccumulating at an implant site in the mammal can readily drain throughthe tissue graft and be removed from the implant site in theperioperative and early postoperative period via surgical drains ornegative pressure wound therapy. The large perforations are sized toenhance mammal tissue anchoring by permitting mammal tissue to compressinto the perforations increasing mammal tissue contact area.

The small and large perforations are arrayed in rows, and the rows aresubstantially parallel to each other. The tissue graft may have aplurality of rows of small perforations and a plurality of rows of largeperforations, and the rows of small perforations alternate with the rowsof large perforations. The large perforations and small perforations aredistributed in staggered rows and columns such that one smallperforation is centered about every four adjacent large perforationsarranged in a substantially square or rectangular manner, and one largeprotrusion is centered about every four adjacent small protrusionsarranged in a substantially square or rectangular manner.

According to one aspect, the plurality of rows of small and largeperforations are equally spaced substantially on the entire surface ofthe tissue graft. The small perforations are spaced about 5 mm to about20 mm apart, and preferably about 7 mm to about 15 mm apart, forexample, about 10 mm apart, as measured between the centers of twoadjacent perforations, for example in the same row. The largeperforations are spaced about 5 mm to about 20 mm apart, and preferablyabout 7 mm to about 15 mm apart, for example, about 10 mm apart, asmeasured between the centers of two adjacent perforations, for examplein the same row. It is anticipated that there may be applications wherethe small and/or large perforations are desired for only certainportions of the tissue graft. For example, the plurality of small andlarge perforations are distributed over about 75%, over about 50%, orover about 25% of the surface of the tissue graft. In addition, theperforations of the same size do not need to be arranged in a row. Forexample, the large perforations may be grouped in certain areas whilethe small perforations may be grouped in other areas, and these largeperforation areas and small perforation areas may be evenly distributedon the entire or partial surface of the tissue graft or in any otherarrangement depending on the clinical applications and desired results.

The row of small perforations and the row of large perforations arespaced about 5 mm to about 20 mm apart, and preferably about 7 mm toabout 15 mm apart, for example, about 10 mm apart, as measured between afirst line connecting the centers of two adjacent small perforations inthe row and a second line connecting the centers of two adjacent largeperforations in the row.

Perforation of the tissue graft is performed using a perforation machinethat comprises a cutting die having a surface of desired dimensions. Thecutting die has on its surface punches that have shapes and sizes thatcorrespond to the predetermined shapes and sizes of the perforations onthe tissue graft to be prepared. The punches are distributed in apattern that corresponds to the predetermined perforation pattern of thetissue graft to be prepared. Suitable perforation machines include thosefor industrial use.

While holes, gaps, or voids have been placed in decellularized tissuespreviously, the holes in the prior art are all the same size and oftenspaced very far apart to allow fluid drainage while minimization theeffect on mechanical properties of the mesh. In the present invention,the differential biological effects of hole sizes have been identifiedand utilized to direct revascularization, tissue generation, and tissueengineering. The creation of specific hole patterns within a device todirect these responses differentially by location within the device is asignificant difference from the prior art.

The present invention provides the ability to control surgical sitefluid drainage, tissue regeneration and wound healing by altering thesize and/or location of perforations in a surgical mesh. It provides theability to control blood flow into a newly generated tissue.

The introduction of holes and void spaces into tissue grafts modulatesthe biologic properties of the implant with different size gaps or holesaffecting the revascularization, tissue generation, and tissueremodeling characteristics. Once implanted, these designed voids arefound to be filled with host generated tissue. Where the cell, vasculardensity, and metabolic/nutritional demand in the host generated tissuewithin the voids is greater than that generated within the microporosityof implanted extracellular matrix (ECM), a macro/microvasculature isobserved to form that is directed specifically towards these fabricatedvoids in the implant. Strategically placing such voids (holes,fenestrations/slits, and/or grooves) is thus a mechanism to inducedirected angiogenesis of a macro/microvasculature. Directed angiogenesiscan be used in tissue engineering and reconstructive surgery tospatially regulate the flow of blood and blood constituents throughout anewly generated tissue, to direct macro/microvasculature towardshost-generated capillary networks found to fill the previouslyfabricated tissue deficits, to provide blood/nutritional support todifferent cell/tissue types placed adjacent to or inside the host tissuefilled tissue deficits, e.g., islet, epithelial, kidney, liver, etc.,and to define the origin of such macro/microvasculature and to supportthe transplantation of the generated tissue to other locations in thepatient for therapeutic or tissue restorative functions by reconnectingto the vascular system via plastic surgery and/or microsurgicaltechniques.

The tissue grafts of the present invention may be used for tissuerepair, regeneration and reconstruction. They can be used as a repair orreplacement device or as a surgical mesh to support soft tissuethroughout the human body. The tissue grafts can be used as a skin wounddressing or a skin replacement tissue. They can also be used for herniarepair, colon, rectal, vaginal and or urethral prolapse treatment;pelvic floor reconstruction; muscle flap reinforcement; lung tissuesupport; rotator cuff repair or replacement; periosteum replacement;dura repair and replacement; pericardia! membrane repair; soft tissueaugmentation; intervertebral disk repair; and periodontal repair. Thetissue grafts may also be used as a urethral sling, laminectomy barrier,or spinal fusion device. They may also serve as a carrier of bioactiveagents, such as growth factors, to generate tissue.

The tissue graft of the present invention may be applied on a patient inneed of tissue repair, regeneration or reconstruction. The smallperforations in the tissue graft facilitates revascularization and cellrepopulation in the patient. The large perforations allow fluiddrainage. The large perforations reduce the occurrence of clotting andgranulation tissue development within the perforations so that surgicaldrains or negative pressure wound therapy can be applied to removeextravascular tissue fluids from the implant site in the perioperativeand early postoperative period.

EXAMPLES

Experimental results show that perforations of different sizes result indifferent host responses.

Example I

Experimental results in hernia repair and intra-abdominal models showedthat perforations above and below a particular size resulted indifferent host responses. The experiments were done on SURGIMENDCollagen Matrix (TEI Biosciences, Inc., Waltham, Mass.), which isderived from fetal or neonatal bovine dermis.

Smaller perforations (<3 mm diameter in 2 mm thick SURGIMEND matrix) arefilled with newly deposited host connective tissue; this new connectivetissue serves as a source of repopulating cells/vessels therebyincreasing the rate of cell repopulation/revascularization of thesurrounding implanted SURGIMEND extracellular matrix.

Larger perforations (>3 mm diameter in 2 mm thick SURGIMEND matrix)tended to stay open/empty of newly deposited host connective tissue.

Example 2

Experimental results in an intramuscular implant model showed thatperforations above and below a particular size result in different hostresponses.

Smaller perforations (<3 mm diameter in 2 mm thick SURGIMEND matrix) arefilled with newly deposited host connective tissue; this new connectivetissue serves as a source of repopulating cells/vessels therebyincreasing the rate of cell repopulation/revascularization of thesurrounding implanted SURGIMEND extracellular matrix.

Larger perforations (>3 mm diameter in 2 mm thick SURGIMEND matrix) werelarge enough that muscle tissue could press into the pore, filling thepore with muscle tissue.

A schematic diagram and visual representation of perforations above andbelow the size threshold is provided in FIG. 2 .

Example 3

The introduction of void spaces in decellularized tissue productsmodulates the biologic properties of the implant. More specifically, thesize of the void spaces or holes affects the revascularization, tissuegeneration, and tissue remodeling characteristics whereby voids aboveand below a critical size result in different host responses. Thisresponse may vary based on the implant location and environmentalsignaling, but generally speaking smaller voids (<3 mm wide in 2 mmthick material) tend to be more rapidly revascularized and filled withnewly deposited host tissue. Larger voids (>3 mm wide in 2 mm thickmaterial) tend to stay open/empty of newly deposited host tissue.

TABLE I Void Implant Environment Volume Mechanical Constraint <14.14mm³ >14.14 mm³ Unconstrained Void filled with newly remained open,deposited, cell dense increased fluid egress host tissue, void acrossthe device contracted in size but not overall implant Uniaxialconstraint collapsed to slits remained open 3 dimensional Void filledwith newly Void closed with constraint deposited, cell dense existingtissue from host tissue, void above and below contracted in size butcompressed into the not overall implant space

The invention may be embodied in other forms without departure from thescope and essential characteristics thereof. The embodiments describedtherefore are to be considered in all respects as illustrative and notrestrictive. Although the present invention has been described in termsof certain preferred embodiments, other embodiments that are apparent tothose of ordinary skill in the art are also within the scope of theinvention.

What is claimed is:
 1. A tissue graft comprising: a sheet of a tissuegraft material having a plurality of rows of small perforations, whichpass through the sheet, and a plurality of rows of large perforations,which pass through the sheet; wherein the small perforations have adiameter that is less than 3 mm and the large perforations have adiameter that is equal to or greater than 3 mm; wherein the tissue graftmaterial is acellular animal tissue; wherein the rows of smallperforations are substantially parallel to the rows of largeperforations; and wherein the rows of small perforations alternate withthe rows of large perforations, such that one small perforation iscentered about every four adjacent large perforations, which arearranged in a substantially square or rectangular manner about the onesmall perforation, and one large perforation is centered about everyfour adjacent small perforations, which are arranged in a substantiallysquare or rectangular manner about the one large perforation.
 2. Thetissue graft of claim 1, wherein the small and large perforations aresubstantially circular.
 3. The tissue graft of claim 1, wherein thesmall perforations are sized to facilitate fibrin provisional matrixformation and granulation tissue development within the smallperforations which, in turn, is a source of blood vessels and cells tofacilitate revascularization and cell repopulation of the tissue graftimplanted on the mammal.
 4. The tissue graft of claim 1, wherein thelarge perforations are sized to reduce an occurrence of fibrinprovisional matrix formation and granulation tissue development withinthe large perforations so that extravascular tissue fluids accumulatingat an implant site in the mammal can readily drain through the tissuegraft and be removed from the implant site in a perioperative and earlypostoperative period via surgical drains or negative pressure woundtherapy.
 5. The tissue graft of claim 1, wherein the large perforationsare sized to enhance mammal tissue anchoring by permitting mammal tissueto compress into the large perforations increasing mammal tissue contactarea.
 6. The tissue graft of claim 1, wherein the large perforations andsmall perforations are distributed in staggered rows and columns.
 7. Thetissue graft of claim 1, wherein the plurality of rows of small andlarge perforations are equally spaced substantially on an entire surfaceof the tissue graft.
 8. The tissue graft of claim 1, wherein the smallperforations are spaced about 5 mm to about 20 mm apart and the largeperforations are spaced about 5 mm to about 20 mm apart, as measuredbetween centers of two adjacent perforations.
 9. The tissue graft ofclaim 1, wherein the rows of small perforations and the rows of largeperforations are spaced about 5 mm to about 20 mm apart.
 10. The tissuegraft of claim 1, wherein: the tissue graft material is abiopolymer-based matrix produced from animal tissue; the tissue graftmaterial is an acellular collagen matrix derived from fetal or neonatalbovine dermis; or the small and large perforations that pass through thesheet are mechanically formed.
 11. The tissue graft of claim 1, whereinthe diameter of the small perforations is about 2 mm.
 12. The tissuegraft of claim 11, wherein the small perforations are spaced apart fromeach other by about 7 mm to about 15 mm and the large perforations arespaced apart from each other by about 7 mm to about 15 mm, as measuredbetween centers of two adjacent perforations.
 13. The tissue graft ofclaim 12, wherein the large perforations and small perforations aredistributed in staggered rows and columns.
 14. A method of repairing orconstructing tissue in a patient, comprising: providing a tissue graftcomprising: a sheet of a tissue graft material and having a plurality ofrows of small perforations, which pass through the sheet, and aplurality of rows of large perforations, which pass through the sheet;wherein the small perforations have a diameter that is less than 3 mmand the large perforations have a diameter that is equal to or greaterthan 3 mm; wherein the tissue graft material is acellular animal tissue;wherein the rows of small perforations are substantially parallel to therows of large perforations; wherein the rows of small perforationsalternate with the rows of large perforations, such that one smallperforation is centered about every four adjacent large perforations,which are arranged in a substantially square or rectangular manner aboutthe one small perforation, and one large perforation is centered aboutevery four adjacent small perforations, which are arranged in asubstantially square or rectangular manner about the one largeperforation; applying the tissue graft to the patient at an implantsite; and allowing revascularization and cell repopulation in thepatient.
 15. The method of claim 14, comprising anchoring the tissuegraft by compressing tissue into the large perforations, therebyincreasing tissue contact area of the tissue graft.
 16. The method ofclaim 14, comprising anchoring the tissue graft by compressing tissueinto the large perforations from above and below the tissue graft. 17.The method of claim 14, wherein the large perforations are devoid ofnewly deposited host tissue.
 18. The method of claim 14, comprisinginducing clotting and granulation tissue development within the smallperforations.
 19. The method of claim 14, comprising: anchoring thetissue graft by compressing tissue into the large perforations fromabove and below the tissue graft; inducing clotting and granulationtissue development within the small perforation; and drainingextravascular tissue fluids that accumulate at the implant site throughthe large perforations; wherein clotting and granulation tissuedevelopment within the large perforations is reduced compared to thesmall perforations.
 20. The method of claim 14, comprising applying asurgical drain or negative pressure wound therapy to the implant site toremove extravascular tissue fluids from the implant site.